Accidental
In today’s edition of The New York Times’ Connections 🔗, one of the categories was “FOUND ON SHEET MUSIC”, which included the word “ACCIDENTAL”.
From Wikipedia 🔗:
an accidental is a symbol that indicates an alteration of a given pitch. The most common accidentals are the flat (♭) and the sharp (♯), which represent alterations of a semitone, and the natural (♮), which cancels a sharp or flat.
According to Etymonline 🔗, the etymology of this usage of “accidental”, which is the same as the etymology of the common sense of “accidental”, is the Latin “accidentalis” referring to a “non-essential quality”.
The musical sense is from 1868; so called because they alter the note without essentially changing the key of the passage.
Moreover, “a nonessential property” is itself one of the additional senses defined by Merriam-Webster 🔗. Which suggests that, for example, one could describe good writing as an accidental of an action film.